The present invention relates to a circuit device for effecting and memorising adjustments to the setting of the controls of a television signal receiver, especially of a colour television receiver; such controls as the volume, brightness, contrast, colour saturation etc. must often be adjusted when changing stations in order to obtain optimum setting of the controls for each station to which the receiver can be tuned in order to account for differences in the signals from each station. Conventionally, television controls are mechanical control systems using potentiometers inserted into the path of the electric signal to be controlled (direct control) or else supplying a D.C. voltage by means of which electronic voltage control is effected (indirect control).
Such mechanical systems have considerable disadvantages, not only from the point of view of durability, since the potentiometers, being mechanical, are subject to wear, but also from that of performance due to non-linearity and discontinuity in the response. Moreover, such mechanical systems are not easily adaptable to the use of remote controls.
For this reason wholly electronic control systems, which operate indirectly, have been recently introduced. These usually comprise a series of counters which are able to count both up and down, each followed by a suitable digital-to-analogue converter. By energising a counter, selected by operation of one of a number of pairs of push buttons, it is possible to increase or reduce the content of this counter and thereby to cause the corresponding control voltage to vary: such variation is discontinuous, but has sufficient resolution for most purposes.
This latter system eliminates many of the disadvantages of the conventional mechanical controls but it is still not wholly satisfactory because, since each station to which a receiver can be tuned usually has modulation characteristics which are different from those of the others, with every change of station it is necessary to readjust, systematically, the controls of the receiver, that is the volume, brightness, contrast (and colour controls in the case of colour transmission).
In fact at present it is possible in many places to receive a large number of transmitter stations (in some cases more than twenty), and hence television receivers have to allow changeover from one station to another with the greatest simplicity. The technical problem which this invention seeks to solve is the provision of a circuit device which is able to effect adjustment of the controls of a receiver upon changes in the tuning thereof to receive signals from different transmitters, which does not suffer from the disadvantages of known systems.